Deeplight

Deeplight is a young adult fantasy novel by Frances Hardinge, her ninth book, released on October 31, 2019, by Macmillan Children's Books. The story takes place in the Myriad, a fictional chain of islands. In the past, the inhabitants worshipped enormous sea creatures they called gods, which fed on human fear from a source beneath the ocean known as the Undersea. Thirty years before the novel begins, these gods turned on one another and destroyed each other in a catastrophe called the Cataclysm. The remains of their bodies are now harvested and used as a durable material called godware.

The protagonist, Hark, lives on the island of Lady's Crave with his best friend, Jelt. After an accident involving a stolen bathysphere, Jelt appears to drown but is revived when a submerged ball of godware reanimates his body and heals his wounds. Hark and Jelt decide to use the ball to heal others in order to repay their debt for the stolen bathysphere. However, Hark soon realizes that prolonged contact with the ball causes strange physical changes, and he worries about Jelt, who refuses to leave it. Hark discovers the ball is actually the heart of one of the gods. He tries to warn Jelt, but it is too late; Jelt has been transformed by the heart into something barely human. In a confrontation, Hark steals the heart but is captured by the Leaguers, a group that wants to revive the age of the gods. They transport the heart to the Undersea to awaken a god-construct made of godware. Jelt appears, merges with the heart and the construct, and becomes empowered by the fear in the Undersea. In the final struggle, Hark accepts that Jelt drowned in the bathysphere accident and has only been kept alive by the god's heart. Hark crushes the heart, killing what remained of Jelt.

Deeplight received positive reviews from The Guardian, Readings, Common Sense Media, and Booklist, including starred reviews from Kirkus and Publishers Weekly. It was nominated for the British Science Fiction Association Award for Best Artwork in 2019, the Lodestar Award in 2020, and was named to the American Library Association's Best Fiction for Young Adults Top Ten in 2021.